The Cartwheel Galaxy
By chance, a collision of two galaxies has created a surprisingly recognizable shape on a cosmic scale. The Cartwheel Galaxy is part of a group of galaxies about 500 million light years away in the constellation Sculptor . Two smaller galaxies in the group are visible on the left of the above photograph . The Cartwheel's rim is an immense ring-like structure 100,000 light years in diameter composed of newly formed, extremely bright, massive stars. When galaxies collide , they pass through each other -- their individual stars rarely come into contact. The galaxies' gravitational fields, however, may be greatly distorted by the collision . In fact, the ring-like shape is the result of the gravitational disruption caused by a small intruder galaxy passing through a large one, compressing the interstellar gas and dust, and causing a wave of star formation wave to move out from the impact point like a ripple across the surface of a pond. In this case, the large galaxy may have originally been a spiral , not unlike our own Milky Way Galaxy , transformed by the collision. Recent astronomical detective work has indicated what has become of the intruder .